The Short Answer
Modern weather apps are remarkably accurate for the next 1-3 days. Beyond that, accuracy drops steadily. By day 10, forecasts are only slightly better than climatological averages.
Accuracy by Time Horizon
| Forecast Window | Temperature Accuracy | Rain Accuracy |
|---|---|---|
| Today | ±1°C | 85-95% |
| Tomorrow | ±1-2°C | 80-90% |
| 3 days | ±2-3°C | 70-80% |
| 5 days | ±3-4°C | 60-70% |
| 7 days | ±4-5°C | 50-60% |
| 10+ days | ±5°C+ | Little better than guessing |
Why Forecasts Get Worse Over Time
Weather is a chaotic system. Tiny differences in initial conditions amplify over time. Edward Lorenz called this the butterfly effect. After about 10 days, those tiny uncertainties have grown so large that specific predictions become meaningless.
Which Apps Are Most Accurate?
Studies consistently show that apps powered by the European Centre for Medium-Range Weather Forecasts (ECMWF) tend to perform best globally. The US Global Forecast System (GFS) is a close second.
Most consumer apps blend multiple models. The best ones weight models dynamically based on which has been performing best in your region.
How to Get the Best Forecast
- Check the forecast the evening before, not three days out
- Look at hourly breakdowns rather than daily summaries
- Compare two or three apps if an important event depends on weather
- Pay more attention to temperature forecasts (more reliable) than rain timing (less reliable)
Weather Tomorrow uses the latest forecast models updated hourly.
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